1. Field of the Invention
The present invention relates to a vibration speaker used in mobile communication terminals including cellular phones and pagers for simultaneously generating a sound and a vibration, and in particular, to transferring a stable vibratory force to a set including a vibration speaker for eliminating a touch sound of a vibrating mass and generating a minimum vibrating force during vibration by expanding inputted frequency bandwidth.
The general principle of generating vibration in a vibration speaker used for cellular phones, pagers, etc. is to use a resonance frequency of a vibration system inside of the vibration speaker.
In this regard, the vibrating mass inside of the vibration speaker performs a vertical movement, and touching phenomenon occurs when the vibration mass collides with objects in the upward and downward directions in accordance with the intensity or frequency of inputted vibration signals. Therefore, certain limitations need to be laid on intensity and frequency of the inputted vibration signals when using the vibration speaker as a vibration generator so as not to cause the touching phenomenon in the upward and downward directions.
FIG. 1 is a cross-sectional view of a conventional vibration speaker. Referring to FIG. 1, the conventional vibration speaker comprises a case 8 having an inner space, a magnet 4 and a voice coil 2 housed in the case 8, and a vibrating plate 1 for generating a sound.
In the conventional vibration speaker constructed above as shown in FIG. 2, electromagnetic force is generated if an alternated current, which is a high frequency, is applied to the voice coil 2 within a magnetic field consisting of an upper plate 3, the magnet 4 seated in a vertical direction, and a yoke 5 through a lead wire (not shown in FIG. 2) from outside. The voice coil 2 performs a vertical movement due to the generated electromagnetic force. At this stage, a sound is generated by a fine vibration of the vibrating plate 1, to which a tip of the voice coil 2 is attached.
Also, if a low frequency signal (preferably of 100-200 Hz) as shown in the left part of FIG. 2 is applied to the voice coil 2, a vibration is generated by triggering a vertical movement of the vibrating mass including the weight 6 and parts constituting the magnetic field suspended on an upper suspension spring 7 and a lower suspension spring 9.
The amount of movement of the vibrating mass varies according to the intensity and frequency of the inputted low frequency signals for generating a vibration. Here, touching phenomenon occurs such that the vibrating mass collides with the vibrating plate 1 and the voice coil 2 at the upper side and other attachments at the lower side.
To limit the vertical movement of the vibrating mass for protecting the collided objects from the touching phenomenon, a stopper structure 6a that can limit the vertical displacement is included in the vibrating mass. Finger stops 8a, 9b are installed at upper and lower sides of the inner wall surface of the case facing the stopper structure 6a. 
Even if the stopper 6a and the finger stops 8a, 8b may be able to protect major parts, the touching phenomenon per se cannot be prevented due to the stopper 6a, and the touching noise is still generated.
Therefore, to prevent the touching phenomenon of the vibrating mass and the noise caused thereby, it is critical to limit the intensity and frequency width of the signals inputted to the voice coil 2, etc.
In other words, as the intensity and the frequency bandwidth of the input signals for generating a vibration, which affect the amplitude of the vibrating mass, should prevent the touching phenomenon and the accompanying noise while satisfying the minimum function of incoming calls, the intensity and the frequency need to be limited.
This means that the amplitude and the inputted frequency bandwidth are determined according to the vibrating characteristics of a product itself constituting the vibration system with the mass and spring. Therefore, the inputted frequency is determined by the natural frequency of the vibration system (xcfx89n=2xcfx80fn), thereby affecting the amplitude of the vibrating mass.
FIG. 10A shows the conventional vibration speaker represented by a simplified vibration system. Assuming that the vibrating mass by the magnet 4, the yoke 5, the upper plate 3 and the weight 6 is simplified into xe2x80x9cmxe2x80x9d, and that the suspension springs 7, 9 are simplified into a spring coefficient xe2x80x9ckxe2x80x9d, the natural frequency of the vibration system constructed as above is determined by the values of xe2x80x9cmxe2x80x9d and xe2x80x9ckxe2x80x9d as follows.
xcfx89n={square root over (k/m)}
Since the natural frequency forming the characteristics of the vibration system is affected by the initial conditions or amplitude, a strict management of the parts related to the vibrating characteristics is required when manufacturing the product in order to resolve the above problem caused by the touching phenomenon. The burden of the managing items is added when assembling the product, thereby increasing the unit cost. Ignorance of these factors results in a product of low quality.
It is, therefore, an object of the present invention to provide a vibration speaker used for mobile communication terminals including cellular phones and pagers that can transfer a stable vibrating force to a set, on which a device is mounted for eliminating a touch sound of a vibrating mass and generating a minimum vibrating force during vibration, by expanding inputted frequency bandwidth.
To achieve the above object, there is provided a vibration speaker for transferring a stable vibrating force to a set, on which a device is mounted for eliminating a touch sound of a vibrating mass and generating a minimum vibrating force during vibration, by expanding inputted frequency bandwidth, the speaker comprising: a case having a space on an inner wall surface; a vibrating plate fixed on an upper end portion of the case at an external tip thereof for generating a sound; a voice coil wound around the vibrating plate so that an upper end thereof can be fixed on the vibrating plate; a plate, an external tip of which is fixed onto a lower end portion of the case; a magnet seated in a vertical direction; an upper plate attached to the magnet for forming a magnetic field; a weight provided on a lower portion of the voice coil to constitute a vibrating mass together with a yoke; a suspension spring for suspending the vibrating mass; and a magneto-rheological fluid having a viscosity inside thereof.
As shown in FIG. 3, the magneto-rheological fluid is positioned between a yoke 15 and a plate 20. The magneto-rheological fluid is, as shown in FIG. 7, a fluid comprising fine magnetic particles 22 having magnetism, and a liquid 24 containing a surfactant 23 surrounding the magnetic particles 22 and oil. The magneto-rheological fluid 21 has characteristics of maintaining a consistent form if laid within the magnetic field of higher than a certain intensity so as not to flow out of or run over the rim. If the magnetic field is formed in the upper plate 13, the magnet 14, the yoke 15, etc. constituting the magnetic field, as shown in FIG. 7, the vibrating mass performs a vertical movement so that the cleft made with the plate 20, which is attached to the lower side of the upper plate 13, becomes narrow due to the vertical movement of the vibrating mass. Because of the facilitation of the magneto-rheological fluid 21 having viscosity as shown in FIGS. 3 and 4, the magneto-rheological fluid 21 is always placed between the vibrating mass and the attachment of the lower side.
The magneto-rheological fluid 21 placed between the vibrating mass and the attachment of the lower side functions as a kind of damper due to the viscosity of itself. The following is an explanation of the function.
FIG. 10B shows a vibrating modeling that simplifies the vibrating speaker according to the present invention. Compared with the conventional structure, FIG. 10B shows that the damper has been added due to the viscosity of the magneto-rheological fluid 21. The vibration system having a damper is affected by a damping force proportional to a velocity as well as by an elasticity of the spring and a gravity of the mass. Thus, the vibrating characteristics are varied as shown in FIG. 9. This means that, the movement of the vibrating system is variable in accordance with an amount of the damping, and the vibration is usually damped when the amount of damping increases compared with the case when no damping exists. In other words, the amplitude is reduced when the amount of damping increases.
As a consequence, no noise is generated owing to no occurrence of the touching phenomenon, and other kinds of noise is also drastically reduced. In terms of the characteristics of the frequency of the vibrating force generated by the vertical movement of the vibrating mass, the intensity of the input signals can also be increased more than the conventional case owing to an increased damping resulted from the viscosity of the magneto-rheological fluid. Thus, the bandwidth of the inputted frequency is widened.
The part identified by dotted lines in FIG. 9 represents the conventional structure, under which the bandwidth of the maximum frequency is narrow. On the other hand, the part identified by a solid line represents characteristics of the present invention having an amplified maximum frequency bandwidth. Therefore, the present invention is characterized in that desired vibrating characteristics can be acquired by preventing the conventional touching phenomenon with proper control of an amount of damping of the vibration system having a damper.